Golf club heads, particularly wooden heads or "metal woods," have a characteristic shape of a generally flat sole plate, a generally rounded top and a generally flat face extending between them, that face being adapted to strike the ball when the club is swung by means of a shaft. The connection between the head and the shaft is by means of a shank and a hosel. For purposes of defining terminology, the shank will be referred to as that structure extending upwardly from the body and the hosel is an extension of the shank. The shank and hosel normally flow from the head body to the connection with the shaft as a unitary structure. Both of these are typically cylindrical. The hosel is normally adapted to receive the shaft internally and the hosel and shaft are secured together in that relationship. By way of further explanation the dictionary definition of a hosel is "a socket in a golf club head into which the shaft is inserted."
By having a round shank and a hosel of sufficient size to receive the shaft therein, a certain amount of mass exists between the golf club head body and the shaft. Also, there is a certain amount of drag on a club having a shank and hosel of this shape, all of which limit the distance a ball may fly when struck with a golf club of the prior art configuration. One limitation is caused by drag which not only limits head speed but also induces instability caused by air flow around the rapidly moving round shank and hosel. Additionally, for a certain swing weight, the size and shape necessary for the conventional shank and hosel limit the mass of the golf club head body.
Swing weight may be thought of as the mass existing at the end of the shaft having to do with the "feel" to the golfer when the golfer swings the club through the position of a ball.